Method of and apparatus for the continuous mining of mineral material by combined drilling, undercutting and shooting operations



July 16, 195.7 A. H. MANDT 2,799,488

METHOD OF AND APPARATUS FOR THE CONTINUOUS MINING CF MINERAL MATERIAL BYCOMBINED DRILLING, UNDERCUTTING AND SHOOTING OPERATIONS Filed May 12,1955 3 Sheets-Sheet 1 INVENTOR. AMBROSE H.MANDT BY DES JARDINS, ROBINSON& KEISER HIS ATTORNEYS 3 Sheets-Sheet 2 llllf/l/l/ A. H. MANDT INVENTOR.AMBROSE H. MANDT DES KARDINS, ROBINSON 8. KEISEP AND SHOOTING OPERATIONSMETHOD OF AND APPARATUS FOR THE CONTINUOUS MINING OF MINERAL MATERIAL BYCOMBINED DRILLING, UNDERCUTTING July 16, 1957 Filed May 12, 1955 HISATTORNEY July 16, 1957 A. H. MANDT 2,799,

METHOD OF AND APPARATUS FOR THE; commuous MINING OF MINERAL MATERIAL BYCOMBINED DRILLING, UNDERCUTTING AND SHOOTING OPERATIONS 3 Sheets-Sheet 3Filed y 12, 1955 V \SQM V m 7%) mm mm Q m v .R E 8 E K 0a N 0 5 m B 0 RS. m D R Y v S 5 ATTORNEYS NIETHOD OF AND APPARATUS FOR THE (IGN-TINUOUS MINING F MENERAL MATERIAL BY COMBINED DRILLING, UNDERCU'ITINGAND SHODTING @PERATIOFE Ambrose H. Mandt, Manton, Ky.

Application May 12, 1955, Serial No. 507,869

19 Claims. (Cl. 2629) This invention relates to a novel method andapparatus for removing coal or other material from a vertical face orwall of limited height. In accordance with my invention, the material isremoved from the face by combined drilling, undercutting and shootingoperations which may be performed either alternately or simultaneouslyas may be found most suitable under the circumstances.

Of recent years, considerable attention has been given to thedevelopment of a fully mechanized mining machine which will operatecontinuously to remove coal from the coal face and deliver it to a minecar or conveyor which then carries it out of the mine. One of themachines of this character with which I am familiar is con structed witha cutter head on which is mounted a series of rotatable cutter arms forremoving the coal from the face and sweeping it onto a conveyor whichdelivers it into the mine cars or onto the conveyor. Where hard, solidcoal is encountered at the face, however, it has been found that thetraction devices of the machine are unable to produce suflicienttractive effort on the floor of the mine room to force the revolvingcutters to dig into the coal face. Accordingly, at times the cuttersWlll merely groove the coal face and will be ineffective to break thecoal therefrom. To overcome this difliculty, I have discovered a way tointermittently shoot the coal as the digging proceeds to therebyfracture the same and insure easy removability of the coal from theface.

Accordingly, it is an object of this invention to provide a method ofcontinuously drilling and shooting the material being mined without thenecessity of removing the drill stem from the bore hole before shootingtakes place.

Another object of the invention is to provide a method of simultaneouslyremoving material from the face and drilling a bore hole therein as themining operation proceeds.

Another object of the invention is to provide a method of continuouslymining coal or other mineral material by simultaneously drilling andundercutting the material and periodically shooting the same to breakdown the material in advance of the face.

Another object of the invention is to provide an improved form ofapparatus for continuously mining coal or other material by combineddrilling, undercutting and shooting operations.

Another object of the invention is to provide a combined shell and drillfor permitting shooting of the material being mined without thenecessity of removing the drill from the bore hole before it is shot.

With these and other objects in view which will become apparent from thefollowing description, the invention includes certain novel proceduresfor facilitating the mining of coal and other mineral materials andcertain novel features of construction and combinations of parts of amining apparatus, the essential elements of which are set forth in theappended claims and a preferred form or embodiment of which willhereinafter be described with reference to the drawings which accompanyand form a part of this specification.

ICE

In the drawings:

type of mining machine to which I have shown my invention applied, therear part of the machine being shown in phantom outline.

Fig. 2 is a front view of the machine shown in Fig. 1 on an enlargedscale.

Fig. 3 is a plan view of the machine shown in Fig. l with the rear partof the machine again shown in phantom outline.

Fig. 4 is a detail view, partially in cross-section, showing the hollowshaft with the cartridge mounted on one end and the drill and shell uniton the other.

Fig. 5 is a detail view showing the forward end ofthe drill and shellunit. 7

Fig. 6 is a cross-sectional view, with the housing removed, of thestructure shown in Fig. 4.

Fig. 7 is a detail view, partially in cross-section, of one of thehigh-pressure swivel fittmgs.

Fig. 8 is a detail, cross-sectional view of the bevel gear drive for thekerf cutter.

Fig. 9 is a diagrammatic view of the high-pressure valve for controllingthe charging and discharging of the cartridge.

As heretofore stated, the present invention includes a new method ofmining coal or other mineral material which consists in drilling boreholes into material at the same time that the material is being cut orbroken away from the face. By combining these operations, the re.-quired number of bore holes are continuously being drilled into thematerial as the cutting and breaking operation proceeds so that theholes are present and ready for shooting at recurring intervals tofracture the coal or other material and thereby facilitate its removalfrom the face.

The invention also includes the method of undercutting the face at thesame time that the bore holes are being drilled therein and the materialis being removed therefrom by the cutting or breaking thereof from theface. Hence, a bottom kerf will be produced simultaneously with thedrilling of bore holes in the face so as to prepare the coal or othermaterial for shooting as the mining operation proceeds. Undercutting ofthe face is desirable where shooting is employed since it provides roomfor expansion of the material and assists in the fracturing thereof.

The invention also includes the method of intermittent shooting of themineral body either simultaneously with the drilling and breakingoperations or at the conclusion of such operations when furtherfracturing and breaking of the material by shooting is required.

The method of the present invention also includes the steps of advancingthe drilling, shooting, undercutting and breaking apparatus toward theface and for removing the broken material from the face and carrying itto the rear of the apparatus where it may be loaded into mine cars andtaken out of the mine.

For the purpose of enabling my novel method of operation to be carriedout expeditiously and in the manner intended, I have devised a miningapparatus which is comprised of several novel features of constructionand combinations of parts not heretofore known or used, so far as I amaware, in mining operations. The specific form of apparatus which I haveinvented to fulfill this purpose is shown in the accompanying drawingsand will now be described in detail though it is to be understood thatother forms of apparatus coming within the scope of the claims appendedhereto might be used for carrying out the method if so desired.

In the drawings I have shown my invention as applied to' a miningmachine of known type which need not be shown or described other than ina very general manner for an understanding of the present invention. Asshown in Figs. 1, 2 and 3, this machine includes a frame on which ismounted a two-section cutting head consisting of an upper row of cuttingor breaker arms 11 and bottom row of cutting or breaker arms 12. Alsocarried by the frame is a conveyor 13 extending lengthwise thereof andrunning from a position beneath the breaker arms to the rear end of themachine where it discharges its burden into a mine car or conveyor forremoval from the mine. Also mounted on the frame of the machine aretramming devices consisting of a pair of endless, track-type treads 1.4by which the machine may be advanced toward the coal face. The machinemay be caused to follow a winding or sinuous seam by tilting the cuttinghead 10 on the frame about a horizontal axis by means of hydraulic jacks17 (Fig. 3). Additional hydraulic jacks 18 (Fig. l) are provided foradjusting the two sections of the cutting head closer t1 gether orfarther apart for adapting the machine to seams of different heights.

In accordance with known practice, the cutting or breaker arms 11 and 12are supported on a series of parallel shafts suitably journaled forrotation in the two sections of the'cutting head. The shafts arearranged to be driven through intermeshing spur gears from powerprovided by hydraulic motors 19 (Fig. 3) which are supplied withhydraulic fluid under pressure from a pump driven by an electric motorin the conventional manner. The drive of the upper and lower breakerarms 11 and 12, respectively, by the two motors is maintained insynchronism by a pair of drive shafts 20 fitted at either end withuniversal joints 21. The shafts 20 are caused to rotate in unison byintermeshing gears contained in a gear case 22 so that the two rows ofbreaker arms driven by motors 19 will be caused to rotate insynchronism.

To this machine, as described above, I have applied the additionalcomponents hereinafter to be described which serve to adapt the machinefor use in carrying out my novel mining method.

In the present embodiment of the invention, the machine is provided withthree combined drill and shell units 25 which, for convenience, are eachsecured to one of the parallel shafts on which the breaker arms 11 aremounted. Each of the breaker arm shafts on which the units 25 aremounted are hollow, one of these shafts being shown in Fig. 6 where itis numbered 26. The three shafts 26 are identical and a description ofone will suffice for all. As shown, the shaft is provided with alongitudinally extending bore 27 which is threaded at its forward(left-hand) end to receive the threaded end of the stem 28 of the drilland shell unit associated therewith. The stem 28 like the shaft 26 ishollow and contains a bore 2? communicately connected with the bore 27of the shaft. The shaft 26 also carries a drive gear 30 which isconnected by intermeshing gears with the other breaker arm shafts of theupper section of the cutting head 10. At its rear end, the shaft 26 isexternally threaded to receive the internally threaded neck 31 of acartridge 32 which is supplied with high-pressure air or gas through aswivel fitting 33.

As shown in Fig. 4, the hollow shaft 26 is, like the other breaker armshafts, journaled in roller bearings 35 supported within a housing 36which forms a part of the upper section of the cutting head. Secured tothe forward face of this housing is a cylindrical cover 37 provided witha hearing or bushing 38 through which the shaft 36 passes. The breakerarm 11 of the particular shaft in question is mounted on the forward endthereof beyond the bushing 38.

Secured to the rear face of the housing 36 is a casing 40 within whichthe cartridge 32 is journaled for rotation by thrust bearings 41 and 42and a sleeve type hearing or bushing 43 received within an extension 44of reduced diameter provided on the rear end of the casing 40 whichengages a neck 45 formed on the rear end of the cartridge. Hence, as theshaft 26 is revolved by means of drive gear 39, the stem 28 of the drilland shell unit 25 will be rotated and the cartridge 32 will rotate withthe shaft 26.

As heretofore mentioned, high-pressure air is supplied to the rear endof the cartridge by the swivel fitting 33. As shown in Fig. 7, theswivel comprises a sleeve 46 which is screwed onto a threaded tenonformed on the rear end of the neck 45. Within the sleeve 46 is a nipple47 mounted for rotation therein by ball bearings 43. The fitting 33 isof a commercially available type and is provided with the customarysealing baffies and gaskets to prevent the escape of high-pressure airfrom the swivel connection provided by the fitting. The nipple 47 isretained within the sleeve 46 by a ring 49 en circling the nipple, and athreaded retaining ring 50 which screws into the end of the sleeve 46.The rear end of the nipple 47 is internally threaded to receive acorrespondingly threaded fitting to which high-pressure air is deliveredto the swivel 33.

As shown in Fig. 3, the three swivels 33 are connected by a commonconduit 5-4 which mechanically ties the swivels together and at the sametime provides means for delivering high-pressure air thereto. Air isdelivered to the conduit 54 by a flexible hose 55 which is connected bya union 56 with a conduit 57 which extends to the rear of the machinewhere it is connected with one of the ports of a high-pressure controlvalve 58. This valve is provided with a handle 59 which may bemanipulated by an operator who is normally stationed at the positionshown by the dot-and-dash circle 60 where he is able to manipulate thecontrols of the machine.

As shown in Fig. 9, the valve 53 may be of any suitable type which willwithstand the high pressures involved and which will provide forselective interconnection of three ports thereon. In the plug-type valveherein shown, the line 57 leading to the cartridge 32 may be selectivelyconnected by manipulation of the handle 59 to a line 62 connected with acompressor unit (not shown). This unit may either be located outside themine or it may be mounted on a movable support so as to enable it tofollow the mining machine as it moves into the seam. Alternatively, theline 57 may be connected with a vent port 63 on the valve by suitablemanipulation of the handle 59 to thereby vent the line 57 to atmosphere.

When the handle 59 of the valve is turned so as to connect thecompressor line 62 with the line 57, the cartridge will be charged withair or gas under high pressure delivered thereto by the compressor.After the cartridge has been thus charged, it may be discharged byturning of the handle to the position in which the line 57 is vented toatmosphere whereupon the highpressure air or gas within the cartridgewill be discharged through a port in the forward end thereof which iscommunicatively connected with the interior of the shaft 26 and stem 28.

The interior construction of the cartridge is shown in Fig. 6, butinasmuch as this device is of a commercial type which is well known tothe mining industry today, the description thereof will be limited to somuch as is necessary for an understanding of the manner in which thisdevice functions to produce the result desired. The interior of thecartridge 32 is hollow so as to provide a pressure chamber 67 forreceiving the high-pressure air or gas from the compressor through theline 57. Extending longitudinally of the cartridge within the chamber 67is a piston rod 68 which is fitted at its forward end with a valve 69adapted to seat against an annular gasket which is backed up by anannular valve seat 70. At its rear end, the piston rod 68 passes througha stationary sealing disc 71 which is provided with a small vent hole72. Secured to the rear end of the rod 68 is a piston 73 which worksloosely within a cylindrical seems bore formed within the neck 45.Mounted upon the forward face of the piston 73 is a plunger leather 75which effects sealing of the piston within the cylinder 74 against theescape of high-pressure air from the space 76 lying between the disc 71and the piston 73.

The operation of this device is as follows:

When high-pressure air or gas from the compressor is delivered to therear end of the cartridge, the piston 73 will be moved forward to closethe valve 69 and seal the chamber 67 against the escape of high-pressureair or gas. The pressure within the chamber will build up gradually asthe air or gas passes around the loosely fitting piston 73 and throughthe vent hole 72 until the pressure within the chamber is equal to thatdelivered by the compressor. When it is desired to discharge the air orgas within the cartridge through the valve 69, the handle 59 of thevalve 58 is turned so as to vent the line 57 to atmosphere and reducethe pressure on the rear face of piston '73 to substantially atmosphericpressure. The high-pressure air or gas trapped in the space 7 6 betweenthe sealing disc 71 and the piston 73 will, smce the area of the pistonis greater than that of the opening in the seat 70, force the piston 73rearwardly, the leather 75 tending to seal the air or gas within thespace 76 against escape. The valve 69 will thereupon be removed from itsseat and the high-pressure air or gas in the chamber 67 permitted todischarge into the hollow shaft 26. This will cause a blast of air orgas to be transmitted through the shaft 26 into the interior of thedrill and shell unit 25. After the cartridge has been discharged, it mayagain be charged by turning the handle of the valve 58 to a position inwhich the compressor line 63 is connected to the line 57 leading to thecartridge.

As shown in Figs. 4 and 5, the stem 28 is provided with a spiral flight80 and a cutting bit 81 of conventional design. The stem 28 is alsoprovided at its forward end with a series of blast ports 82 which arearranged circumferentially around the stem. Hence, when the blast of airor gas is released from cartridge 32, it will pass through the hollowshaft 26 and stem 28 and issue from the ports 82 with explosive forceand cause fracturing of the coal or other material being mined. Toincrease the effectiveness of the blasting or shootmg operation and toprovide room for the coal to expand, the machine is provided with a pairof kerf cutters 85 each of which consists of a chain guide 86 having theshape of a hollow triangle and suitably secured to the cutter head atits rear end. Running on each guide 86 is a cutter chain 87 whichcarries a series of staggered cutter bits 88 (see also Fig. 2) forcutting a kerf in the coal as the chain travels around the guide 86.Suitable bracing 89 may be provided for the chain guides 86 to providethe necessary strength thereto.

The power required to drive each of the chains 82 may conveniently bederived from the shafts of the outermost breaker arms 12 of the bottomsection of the cutting head. As shown in Fig. 8, a breaker arm shaft 90of one of said arms is journaled within a housing 91 by roller bearings92. The shaft has fixed thereon a spur gear 93 which meshes with anadjoining gear in the gear train which drives the breaker arms 12 andcauses these arms to be rotated in unison by power derived from thehydraulic motors 19. Secured to the forward face of the housing 91 is agear casing 94 in the bottom of which a jack shaft 95 is journaled forrotation by roller bearings 96. The shaft 95 is driven from the shaft 90by a pair of meshing bevel gears 97 and 98 and the shaft carries at itslower end a chain sprocket 99 which engaged with the cutter chain 87 andcauses it to be driven as the shaft 90 rotates. An oil seal 100 may beprovided in the bottom of the gear casing 94 to seal the openingtherein, through which the shaft 95 passes, against the escape of oil.The kerf cutters 85 are supported from the framework of the cutting head10 so as to tilt with the head and thereby follow any deviations in theseam in the same manner as the drill and shell units 25 and the breakerarms 11 and 12.

The operation of the mining machine heretofore described is as follows:

The machine is trammed toward the coal face 101 (Fig. 1) in the usualmanner by means of the tracks 14. Thereupon, the kerf cutters and thedrill and shell units 25 penetrate into the face 101 (Fig. 1) of thecoal or other material being mined and the breaker arms 11 and 12 engagethe face and break the coal loose therefrom. To shoot the coal andthereby assist the breaker arms in removing the coal from the face, theoperator of the machine, who is normally stationed at 60 (Fig. 3), turnsthe valve 50 to connect the line 62 from the compressor with the line 57to the cartridge 32 and, after the cartridge has been charged, turns thehandle to vent the line 5"? to atmosphere. As previously explained,thiscauses the valve within the cartridge to open and permits a blast ofhigh-pressure air or gas to pass through the hollow shaft 26 and stem 28of the drill and to issue with explosive force through the blast ports82 (Fig. 5). Since the coal has been undercut by the kerf cutters 85slightly in advance of the end of the drill, the coal will be readilyfractured and knocked down so that the arms 11 and 12 can readily cleanup the face and remove any coal which was not knocked down by the blast.The conveyor 13 of the machine (Fig. 2) has its forward end disposedimmediately behind the breaker arms where it will be in position toreceive the broken coal and transport it to the rear of the machine. Asindicated by the arrows in Fig. 2, the breaker arms turn inwardly so asto sweep the coal in toward the conveyor.

After the machine has advanced a sufiicient distance to again bring thebreaker arms into contact with solid coal, the operator may againmanipulate the valve 58 to shoot the coal and thereby permit rapidadvance of the machine into the seam. With this means of fracturing andbreaking the coal independently of the action of the breaker arms, lessslack will be produced and a better quality of coal obtained.

The shooting operation may be performed while the drills and kerfcutters are operating or, if desired, the operator may stop theseelements at the time of shooting so as to reduce the strain on themachine. In either event however rapid, economical mining of coal orother mineral material which is susceptible to this form of mining willbe obtained.

Having thus described my invention in connection with one possible formof apparatus and having used, therefore, certain specific terms andlanguage herein, it is to be understood that the present disclosure isillustrative rather than restrictive and that changes and modificationsmay be resorted to without departing from the spirit or scope of theclaims that follow.

What I claim as new and useful and desire to secure by United StatesLetters Patent, is:

l. A mobile mining machine comprising a frame, a cutting head on saidframe and including a plurality of breaker arms mounted on a pluralityof rotatable shafts arranged in substantially parallel relationship andso positioned with respect to one another that upon rotation of saidshafts substantially coplanar circles are described by said breakerarms, a bore hole auger mounted on at least one of said shafts in axialalignment therewith for drilling a bore hole in the material being minedin advance of said breaker arms, said auger extending a sufficientdistance in advance of said breaker arms to provide a bore hole ofsufficient depth to enable additional material tobe blasted loose afterthe breaker arms have cleaned off the loose material from the face, andpower driven means for advancing the machine toward the face of thematerial.

2. The mining machine of claim 1 including a kerf cutter supported onsaid frame for undercutting the mate- 7 rial being mined in advance ofsaid breaker arms and below said auger.

3. The mining machine of claim 2 wherein said kerf cutter includes aloop-shaped chain guide that is open in the center so as to provide roomfor expansion of the material when it is shot with the kerf cutter inplace beneath the material. u

4. A drilling and blasting device for use in min ng operationscomprising a frame for supporting said device, a hollow auger rotatablymounted on said frame for drilling a bore hole in the face of thematerial being mined, blast ports in the forward end of said auger,power means for rotating said auger, a cartridge adapted to be chargedwith air or gas under pressure and having a dis charge orifice throughwhich the air or gas may be released, and means communicativelyconnecting said discharge orifice with the rear end of said auger forcausing the blast of air or gas from said cartridge to be delivered tothe forward end of said auger where it passes through said blast portsinto the bore hole.

5. The device of claim 4 wherein said cartridge is rigidly secured tothe rear end of said auger so as to rotate therewith during drilling andshooting operations.

6. The device of claim 4 including a compressed air line for supplyinghigh pressure air to said cartridge for charging the same, and a swivelfitting for connecting said air line to the rotatable cartridge topermit charging of the cartridge while said drill is rotated.

7. A drilling and blasting device for use in mining operationscomprising a drill having tubular drill stern, a cutting bit on theforward end of said stem for drilling into the material being mined, aspiral flight on said stem for removing the material loosened by thebit, means for delivering a blast of air or gas into the rear end ofsaid stern, and a plurality of circumferentially arranged blast portspassing through the wall of the stem at the forward end thereof forconducting the air or gas delivered into the stem into the end of thebore hole.

8. A mobile mining machine comprising a frame, power operated means onsaid frame for removing material from the face, a hollow auger rotatablymounted on said frame and projecting forwardly thereof for drilling abore hole into the material being mined, a plurality of blast holes inthe forward end of said auger, power means for rotating said auger,means communicatively connected with the rear end of said auger fordelivering a blast of air or gas through said auger and said blast holesinto the bore hole to fracture the material being mined, a kerf cuttersupported on said frame for undercutting the solid material in advanceof said moving means and below said auger, and power means for trarnmingthe machine toward the face.

9. A mobile mining machine comprising a frame, a cutting head on saidframe having a plurality of breaker arms mounted on a plurality ofrotatable shafts arranged in substantially parallel relationship on saidframe and so positioned with respect to one another that upon rotationof said shafts substantially coplanar circles are described by saidbreaker arms, a hollow auger rotatably mounted on said frame fordrilling a bore hole in the material being mined in advance of saidbreaker arms, power means for rotating said auger, a plurality of blastholes in the forward end of said auger, means communicatively connectedwith the rear end of said auger for delivering a blast of air or gasthrough said auger and said blast holes into the bore hole to fracturethe material being mined, and power means for tramming the machinetoward the face.

10. The mining machine of claim 9 including a kerf cutter on said framefor undercutting the solid material in advance of said breaker arms andbelow said auger.

11. The method of removing material from the face of an underground seamwhich consists in breaking the material away from the face of the seamand simultaneously drilling a bore hole into the seam beyond the face,and periodically shooting the material as the mining operation proceedsto fracture the material and facilitate its removal from the face.

12. The method of claim 11 wherein shooting of the material is performedsimultaneously with the drilling and breaking operations to therebyenable continuous mining of the material.

13. The method of claim 11 wherein the material being mined is undercutbelow the bore hole simultaneously with the breaking and drillingthereof.

14. The method of claim 13 including conveying the broken material awayfrom the face simultaneously with the breaking. drilling andundercutting operations.

15. A mobile mining machine comprising a frame, a cutting head on saidframe and including a plurality of breaker arms mounted on a pluralityof rotatable shafts arranged in substantially parallel relationship andso positioned with respect to one another that upon rotation of saidshafts substantially coplanar circles are described by said breakerarms, a bore hole auger mounted on at least one of said shafts in axialalignment therewith for drilling a bore hole in the material being minedin advance of said breaker arms, said auger and its associated shafteach being of tubular construction so as to provide a tubiform passageextending from the rear end of said shaft to the forward end of saidauger, means for producing a blast of air or gas, means communicativelyconnecting said means with the passage at the rear end of said shaft,and means for advancing the machine toward the face of the material.

16. The mining machine of claim 15 wherein said blast producing meansincludes a cartridge fixed to the rear end of said shaft and rotatabletherewith.

17. The mining machine of claim 16 including an air line supported onsaid frame, and a swivel fitting communicatively connecting said airline with said cartridge so as to permit said cartridge to rotaterelative to said air line.

18. The mining machine of claim 17 including means for venting the airline to atmosphere after the cartridge has been charged to therebydischarge the cartridge and cause a blast of air or gas to issue fromthe forward end of said auger.

19. The mining machine of claim 8 wherein said kerf cutter includes aloop-shaped chain guide that is open in the center so as to provide roomfor expansion of the material when it is shot with the kerf cutter inplace beneath the material.

References Cited in the file of this patent UNITED STATES PATENTS307,379 Craven Oct. 28, 1884 1,315,271 Young Sept. 9, 1919 1,408,975Black Mar. 7, 1922 1,603,621 McKinlay Oct. 19, 1926 1,726,963 McKinlaySept. 3, 1929 2,083,981 Armstrong June 15, 1937 2,151,328 Noble Mar. 21,1939 2,281,503 Levin Apr. 28, 1942 2,520,040 Levin Aug. 22, 19502,562,841 Compton July 31, 1951 2,694,562 Synder et a1. -e Nov. 16, 1954

